This report presents the findings of a geologic and geotechnical evaluation of a landslide at the Yukon River bridge (the E.L. Patton Bridge). The Yukon River bridge landslide occurred in fall 2012 between approximately 375 and 575 feet west of the bridge. Although there was no damage to the bridge foundation, the landslide's close proximity to the bridge and concerns over additional failures prompted multiple evaluations, including landslide documentation, drainage assessments, and geotechnical studies. This report was prepared to convey the general characteristics of the rock mass, characteristics of rock discontinuities, and the geomorphic expression of the 2012 landslide in the vicinity of the bridge. We determined that the fractured bedrock and steep slopes in the bridge vicinity are prone to slope failure. However, this assessment should be considered preliminary and should not be used to determine areas of potential future slope instabilities. A significant amount of additional exploration and slope stability analysis is required to fully understand the landslide hazard in the area of the bridge, as well as the potential for reactivation and/or expansion of the 2012 landslide into adjacent slopes.

Supplemental_Information:

The geospatial data file provided in this digital data distribution package is a compilation of the manuscript tables 1 and 2. The table headers and data organization have been slightly modified to make the data readily accessible to users who wish to view outcrop locations and descriptions via GIS or other software. The DGGS metadata standard extends the FGDC standard to include elements that are required to facilitate our internal data management. These elements, referred to as "layers," group and describe files that have intrinsic logical or topological relationships and correspond to subdirectories within the data distribution package. The metadata layer provides the metadata, codesets, or other documentation files applicable to all layers. Attribute information for each data layer is described in this metadata file under the "Entity_and_Attribute_Information" section. Data layer contents: >sample-location-details: GPS coordinates and rock mass properties for each outcrop field station.

The horizontal datum used is World Geodetic System of 1984.
The ellipsoid used is World Geodetic System of 1984.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257223563.

General assessed compressive strength of rock at the station, classification parameters and a delimited list of options are provided in data sheet template.
(Source: Alaska Division of Geological & Geophysical Surveys)

General size of the rock blocks that are defined by outcrop fabric; classification parameters and a delimited list of options are provided in data sheet template.
(Source: Alaska Division of Geological & Geophysical Surveys)

Discontinuity is a collective term used here to describe breaks in the outcrop surface; these may include: joints, fractures, bedding planes, rock cleavage, foliation, shear zones etc. This value provides a count of intersecting discontinuities found at each outcrop.
(Source: Alaska Division of Geological & Geophysical Surveys)

This report presents the findings of a geologic and geotechnical evaluation of a landslide at the Yukon River bridge, conducted by the State of Alaska, Division of Geological & Geophysical Surveys (DGGS) through a reimbursable services agreement with the State of Alaska Department of Transportation & Public Facilities (ADOT&PF). De Anne S. P. Stevens provided a technical review of the report.

This report was prepared to convey the general characteristics of the rock mass, characteristics of rock discontinuities, and the geomorphic expression of the 2012 landslide in the vicinity of the Yukon River bridge. However, this assessment should be considered preliminary and should not be used to determine areas of potential future slope instabilities. A significant amount of additional exploration and slope stability analysis is required to fully understand the landslide hazard in the area of the bridge, as well as the potential for reactivation and/or expansion of the 2012 landslide into adjacent slopes.

Geotechnical - geomorphic observations and preliminary interpretation - The Yukon River bridge landslide field review was performed August 25-29, 2013, by Rich Koehler, Karri Sicard, and Eleanor Spangler of DGGS and Richard 'Dick' Reger of Reger's Geologic Consulting. Bedrock outcrops along the base of the Yukon River bluff were inspected for the presence of faults, fractures, shears or weathering zones, and/or other features that could provide information from which to infer subsurface conditions of bedrock farther upslope. Quantitative descriptions of rock mass and discontinuity data are based on the methodology of Barton (1978). Rock mass and discontinuity survey data sheets from the Alaska Field Rock Classification and Structural Mapping Guide (ADOT&PF, 2003) were used to record the field observations. Key rock characteristics that were documented include lithology, color, grain size, field compressive strength, rock mass fabric, block size, and state of weathering. Discontinuity surveys at each outcrop station include information on type of discontinuity, dip, dip direction, persistence, termination, aperture, nature of filling, strength of filling, surface roughness, surface shape, waviness, joint roughness coefficient, and presence of water. Detailed definitions for each of these parameters are provided in ADOT&PF (2003). Discontinuity orientations were measured with a Brunton compass, using standard geologic field techniques. We compiled the field data and LiDAR observations into a preliminary report that summarizes the general characteristics of the rock mass, characteristics of rock discontinuities, and the geomorphic expression of the 2012 landslide and the surrounding area.

The attributes listed in this dataset were transcribed from field-data collection sheets. The field-data sheets were also scanned and included as an appendix to the manuscript. The geologic interpretations presented in this report have undergone technical review by a geologist of comparable technical expertise. We incorporated the reviewer's suggestions into the final draft when deemed appropriate.

We assigned a "station number" to each outcrop discussed in this report. Near the center of each outcrop, we recorded a single GPS waypoint to approximate the location of each "station." A station number (and GPS waypoint) was not recorded for the area between the stations 10 and 11. However, we did record observations in this area.

Users should note that this table is a compilation of the information provided in tables 1 and 2 to the manuscript. These tables provide only the outcrop locations and rock mass values. To see all of the outcrop measurements and descriptions, users should refer to the field-data sheets (see Appendix B of the manuscript).

This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).

Use_Constraints:

Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological &amp; Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.

The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.

DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media by mail, phone, fax, or email from the DGGS Fairbanks office. To purchase this or other printed reports and maps, contact DGGS by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for the exact shipping amount.